Synthesis of early transition metal and non-equilibrium intermetallic nanoparticles using n-butyllithium

Open Access
Author:
Bondi, James Fumiya
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
April 27, 2012
Committee Members:
  • Raymond Edward Schaak, Dissertation Advisor
  • John V Badding, Committee Member
  • Mary Beth Williams, Committee Member
  • Michael Anthony Hickner, Committee Member
Keywords:
  • nanoparticle
  • n-butyllithium
  • early transition metal
  • non-equilibrium
  • intermetallic
  • solid state
Abstract:
Over the past decade, the role of inorganic nanomaterials has become an essential cornerstone for modern research applications. Despite these applications becoming progressively more advanced, the field of nanoscience is dependent on a material’s physical and chemical properties which are affected by factors such as size, shape, composition, and crystal structure. One synthetic approach to yield inorganic nanomaterials with great control is solution-based methods, particularly the reduction of metal salt precursors. Non-equilibrium phases and early transition metals represent one class of materials that may result in new and enhanced properties at the nanoscale but are challenging to synthesize. In this dissertation, I present my studies on synthesizing non-equilibrium intermetallics and early transition metal nanoparticles using n-butyllithium and solution-based methods. By utilizing a template-driven approach, I first report an optimized synthesis for the non-equilibrium L12-type Au3M1-x (M = Fe, Co, or Ni) intermetallics with morphological, compositional, and structural control. Modifying a previous n-butyllithium procedure, it was possible to identify key variables (solvent, order of reagent addition, stabilizer, and heating rate) which led to the generation of high phase purity and increased sample sizes. Aliquot studies showed that the intermetallic nanoparticles were formed through the initial nucleation of Au nanoparticles, followed by subsequent incorporation of the 3d transition metal. Property studies of the non-equilibrium phases found that Au3Fe1-x and Au3Co1-x nanoparticles are superparamagnetic with TB = 7.9 K and 2.4 K, respectively, while Au3Ni1-x is weakly paramagnetic down to 1.8 K. Elemental analysis by energy dispersive X-ray spectroscopy and refinement of electron diffraction patterns confirmed Au3Fe1-x with a composition of approximately Au3Fe0.7. The 3d transition metal deficiency in the non-equilibrium Au3M1-x phases was studied by reacting Au nanoparticle seeds with n-butyllithium. The reaction yielded the thermodynamically stable phase Au3Li, a polar intermetallic which adopts the L12 structure type. Interestingly, the Au3Li nanoparticles decompose in water to regenerate Au. The Au3Li phase gives insight to a plausible template-driven reaction pathway for the non-equilibrium Au3M1-x phases. The synthetic achievement of both non-equilibrium phases and polar intermetallics shows that n-butyllithium is capable of affecting nucleation kinetics and lithium intercalation. Finally, ¬n-butyllithium was used as a strong reducing agent in the solution-based synthesis of elemental Mn nanoparticles. The particles were synthesized using air-free techniques by reacting n-butyllithium with MnCl2 and oleic acid in diphenyl ether. The nanoparticles were found to adopt the α-Mn structure and contained a thin amorphous MnO layer bound by oleate ligands to help render them air-stable. Unlike antiferromagnetic bulk Mn, the as-made nanoparticles were paramagnetic. With little modification, crystalline Mo and amorphous W nanoparticles were synthesized using the same n-butyllithium procedure. Using the thermal decomposition of metal-carbonyls was shown to yield W, Mo-based alloys, and tetrapod-like MnO nanoparticles.